This invention provides silicon nitride compositions from which bodies of near theorectical density can be produced by cold pressing and sintering and by hot pressing.
In general, silicon nitride by itself has limited usage. In order to produce materials for turbines, cutting tools, wear parts and the like, composites are needed which can be pressed to near theoretical density, that is greater than about 96% of the theoretical density. U.S. Pat. Nos. 3,950,464 and 3,953,221 cite compositions of silicon nitride and sintering aids such as yttrium oxide and aluminum oxide to aid in densification. However, with the use of yttrium oxide, the material cannot be cold pressed and sintered to near theoretical density.
The process of this invention involves the use of silicon nitride and hard materials with lanthanum or lanthanum aluminum compounds as densifying agents which can be cold pressed and sintered or hot pressed to near theoretical density.